Laserfiche WebLink
Pond 011 was initially designed for the 2000 Permit Amendment. The pond was constructed in <br />2007. The as built report is included in attachment 2.05.3(3) -21. Due to the decision by WFC to <br />eliminate Pond 010, Ponds 011 and 013 will receive a greater drainage area. This revised design <br />of Pond 011 will demonstrate thatthe as builtpond is sufficientto handle the revised drainage area. <br />Pond 011 is a partially incised pond designed to contain the flow from a 10 year 24 hour storm <br />below the emergency spillway. the valve on the principal spillway pipe is normally held shut. The <br />principal spillway design is an 18 -24" diameter CMP or other pipe which will have a valve on the <br />entrance. This pipe will be stopped down in the inlet side to a 6" valve which will be controlled by <br />a wheel on the pond embankment. During normal conditions, the valve will be shut to provide 24 <br />hour detention time for each pond during the large events. When a large event occurs, the operator <br />will wait a minimum of 36 hours after the storm has ceased to check the water still detained by the <br />pond. An Imhoff cone will only be used to determine if the water can be discharged. If an Imhoff <br />cone shows that the water meets the effluent standard of 0.5ml settleable solids per liter, the valve <br />will be opened until the water has dissipated to the valve level. It will then be shut to allow detention <br />time for subsequent storms. Full sampling and laboratory analyses of the discharge will take place <br />for all discharges, according to the NPDES permit. <br />Pond 011 - Proposed Design <br />Pond 011 has been re- designed for the Permit Revision of 2009. The drainage basins in both pre <br />mine and post mine situations have changed. <br />Design Parameters: <br />• Since the post mine drainage area is larger than the pre mine, but does not involve pit <br />pumping, the post mine condition and the pre mine condition need to be compared to <br />determine the worst case. The pre -mine drainage area is 155.43 acres while the post mine <br />area is 166.1 acres. <br />• Primary spillway riser will have 2 partially opened 6 inch gate valves two feet from the base <br />(5612' elevation) so surface water will be mixed with pond bottom water to better mix the <br />pit pump water for water quality purposes. <br />• There will be an 24 inch Riser /Barrel Primary Discharge with the two 6" weep hole openings <br />with gate valves described above plus an open channel, lined and riprapped Emergency <br />Revised February 2010 (PR06) Attachment 2.05.3(3) -22 -2 <br />